class Solution {
  public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
      int complement = target - nums[i];
      if (map.containsKey(complement))
          return new int[] { map.get(complement), i };
      map.put(nums[i], i);
    }
    throw new IllegalArgumentException("No two sum solution");
  }
}